High intensity, high total energy, and well collimated ion beams are utilized in a variety of applications, particularly in ion implantation processes such as in doping semiconductors and implanting ions to passivate metal surfaces. An ion accelerator system which is commonly used includes an extraction grid or electrode with a narrow slit for extracting a slit-like ion beam, followed by accelerator and decelerator electrodes, and with a potential of many kilovolts between the extraction and accelerator electrodes to produce an accelerated ion beam. Experience has shown that such accelerator systems are limited in beam intensity and focusing, which results in excessively long implantation process times in many applications. An ion beam accelerator system which could produce higher beam current densities with high efficiency and good collimation, would be of value in ion implantation applications, as well as other applications which utilize ion beams.